Sodium nitrite downregulates vascular NADPH oxidase and exerts antihypertensive effects in hypertension

Alternative Additives for Organic and Natural Ready-to-Eat Meats to Control Spoilage and Maintain Shelf Life: Current Perspectives in the United States

Food additives are employed in the food industry to enhance the color, smell, and taste of foods, increase nutritional value, boost processing efficiency, and extend shelf life. Consumers are beginning to prioritize food ingredients that they perceive as supporting a healthy lifestyle, emphasizing ingredients they deem acceptable as alternative or "clean-label" ingredients. Ready-to-eat (RTE) meat products can be contaminated with pathogens and spoilage microorganisms after the cooking step, contributing to food spoilage losses and increasing the risk to consumers for foodborne illnesses. More recently, consumers have advocated for no artificial additives or preservatives, which has led to a search for antimicrobials that meet these demands but do not lessen the safety or quality of RTE meats. Lactates and diacetates are used almost universally to extend the shelf life of RTE meats by reducing spoilage organisms and preventing the outgrowth of the foodborne pathogen Listeria monocytogenes. These antimicrobials applied to RTE meats tend to be broad-spectrum in their activities, thus affecting overall microbial ecology. It is to the food processing industry's advantage to target spoilage organisms and pathogens specifically.

Dietary Nitrate from Plant Foods: A Conditionally Essential Nutrient for Cardiovascular Health

Under specific conditions, such as catabolic stress or systemic inflammation, endogenous nutrient production becomes insufficient and exogenous supplementation (for example, through dietary intake) is required. Herein, we propose consideration of a dietary nitrate from plant foods as a conditionally essential nutrient for cardiovascular health based on its role in nitric oxide homeostasis. Nitrate derived from plant foods may function as a conditionally essential nutrient, whereas nitrate obtained from other dietary sources, such as drinking water and cured/processed meats, warrants separate consideration because of the associated health risks. We have surveyed the literature and summarized epidemiological evidence regarding the effect of dietary nitrate on cardiovascular disease and risk factors. Meta-analyses and population-based observational studies have consistently demonstrated an inverse association of dietary nitrate with blood pressure and cardiovascular disease outcomes. Considering the available evidence, we suggest 2 different approaches to providing dietary guidance on nitrate from plant-based dietary sources as a nutrient: the Dietary Reference Intakes developed by the National Academies of Sciences, Engineering, and Medicine, and the dietary guidelines evaluated by the Academy of Nutrition and Dietetics. Ultimately, this proposal underscores the need for food-based dietary guidelines to capture the complex and context-dependent relationships between nutrients, particularly dietary nitrate, and health.

Local delivery of nitric oxide prevents endothelial dysfunction in periodontitis

AIMS

Increased cardiovascular disease risk underlies elevated rates of mortality in individuals with periodontitis. A key characteristic of those with increased cardiovascular risk is endothelial dysfunction, a phenomenon synonymous with deficiencies of bioavailable nitric oxide (NO), and prominently expressed in patients with periodontitis. Also, inorganic nitrate can be reduced to NO in vivo to restore NO levels, leading us to hypothesise that its use may be beneficial in reducing periodontitis-associated endothelial dysfunction. Herein we sought to determine whether inorganic nitrate improves endothelial function in the setting of periodontitis and if so to determine the mechanisms underpinning any responses seen.

METHODS AND RESULTS

Periodontitis was induced in mice by placement of a ligature for 14 days around the second molar. Treatment in vivo with potassium nitrate, either prior to or following establishment of experimental periodontitis, attenuated endothelial dysfunction, as determined by assessment of acetylcholine-induced relaxation of aortic rings, compared to control (potassium chloride treatment). These beneficial effects were associated with a suppression of vascular wall inflammatory pathways (assessed by quantitative-PCR), increases in the anti-inflammatory cytokine interleukin (IL)-10 and reduced tissue oxidative stress due to attenuation of xanthine oxidoreductase-dependent superoxide generation. In patients with periodontitis, plasma nitrite levels were not associated with endothelial function indicating dysfunction.

CONCLUSION

Our results suggest that inorganic nitrate protects against, and can partially reverse pre-existing, periodontitis-induced endothelial dysfunction through restoration of nitrite and thus NO levels. This research highlights the potential of dietary nitrate as adjunct therapy to target the associated negative cardiovascular outcomes in patients with periodontitis.

Sirtuin1 inhibitor attenuates hypertension in spontaneously hypertensive rats: role of Giα proteins and nitroxidative stress

BACKGROUND

We recently showed that vascular smooth muscle cells (VSMCs) from spontaneously hypertensive rats (SHR) exhibit overexpression of Sirtuin1 (Sirt1) that contributes to the enhanced expression of Giα proteins implicated in the development of hypertension in SHR.

METHOD

The present study investigated if the inhibition of Sirt1 could also ameliorate hypertension in SHR and explore the underlying molecular mechanisms. For this study, a selective inhibitor of Sirt1, EX-527 (5 mg/kg of body weight), was injected intraperitoneally into 8-week-old SHR and age-matched Wistar Kyoto (WKY) rats twice per week for 3 weeks. The blood pressure (BP) and heart rate was measured twice a week by the CODA noninvasive tail cuff method.

RESULTS

The high BP and augmented heart rate in SHR was significantly attenuated by EX-527 treatment, which was associated with the suppression of the overexpression of Sirt1 and Giα proteins in heart, VSMC and aorta. In addition, the enhanced levels of superoxide anion, NADPH oxidase activity, overexpression of NADPH oxidase subunits and FOXO1 were attenuated and the decreased levels of endothelial nitric oxide synthase (eNOS), nitric oxide and increased levels of peroxynitrite (ONOO-) and tyrosine nitration in VSMC from SHR were restored to control levels by EX-527 treatment. Furthermore, knockdown of FOXO1 by siRNA also attenuated the overexpression of Giα-2 and NADPH oxidase subunit proteins and restored the decreased expression of eNOS in VSMC from SHR.

CONCLUSION

These results suggest that the inhibition of overexpressed Sirt1 and its target FOXO1 through decreasing the enhanced levels of Giα proteins and nitro-oxidative stress attenuates the high BP in SHR.

Mechanistic Insights into Inorganic Nitrite-Mediated Vasodilation of Isolated Aortic Rings under Oxidative/Hypertensive Conditions and S-Nitros(yl)ation of Proteins in Germ-Free Mice

The prevalence and clinical importance of arterial hypertension are still growing. Inorganic nitrite (NO₂^-) represents an attractive dietary antihypertensive agent, but its metabolism and mode of action, which we aimed to investigate with the present study, are not completely understood. Isolated aortic rings from rats were treated ex vivo with oxidants, and rats were infused in vivo with angiotensin-II. Vascular responses to acetylcholine (ACh) and nitrite were assessed by isometric tension recording. The loss of vasodilatory potency in response to oxidants was much more pronounced for ACh as compared to nitrite ex vivo (but not in vivo with angiotensin-II). This effect may be caused by the redox regulation of conversion to xanthine oxidase (XO). Conventionally raised and germ-free mice were treated with nitrite by gavage, which did not improve ACh-mediated vasodilation, but did increase the plasma levels of S-nitros(yl)ated proteins in the conventionally-raised, but not in the germ-free mice. In conclusion, inorganic nitrite represents a dietary drug option to treat arterial hypertension in addition to already established pharmacological treatment. Short-term oxidative stress did not impair the vasodilatory properties of nitrite, which may be beneficial in cardiovascular disease patients. The gastrointestinal microbiome appears to play a key role in nitrite metabolism and bioactivation.

The Role of NRF2 in Obesity-Associated Cardiovascular Risk Factors

The raising prevalence of obesity is associated with an increased risk for cardiovascular diseases (CVDs), particularly coronary artery disease (CAD), and heart failure, including atrial fibrillation, ventricular arrhythmias and sudden death. Obesity contributes directly to incident cardiovascular risk factors, including hyperglycemia or diabetes, dyslipidemia, and hypertension, which are involved in atherosclerosis, including structural and functional cardiac alterations, which lead to cardiac dysfunction. CVDs are the main cause of morbidity and mortality worldwide. In obesity, visceral and epicardial adipose tissue generate inflammatory cytokines and reactive oxygen species (ROS), which induce oxidative stress and contribute to the pathogenesis of CVDs. Nuclear factor erythroid 2-related factor 2 (NRF2; encoded by Nfe2l2 gene) protects against oxidative stress and electrophilic stress. NRF2 participates in the regulation of cell inflammatory responses and lipid metabolism, including the expression of over 1000 genes in the cell under normal and stressed environments. NRF2 is downregulated in diabetes, hypertension, and inflammation. Nfe2l2 knockout mice develop structural and functional cardiac alterations, and NRF2 deficiency in macrophages increases atherosclerosis. Given the endothelial and cardiac protective effects of NRF2 in experimental models, its activation using pharmacological or natural products is a promising therapeutic approach for obesity and CVDs. This review provides a comprehensive summary of the current knowledge on the role of NRF2 in obesity-associated cardiovascular risk factors.

Mediterranean diet and cognitive function: From methodology to mechanisms of action

The traditional Mediterranean diet (MedDiet), rich in minimally processed plant foods and fish, has been widely recognized to be one of the healthiest diets. Data from multiple randomized clinical trials have demonstrated its powerful effect against oxidative stress, inflammation and the development and progression of cardiovascular disease, type 2 diabetes, and other metabolic conditions that play a crucial role in the pathogenesis of neurodegenerative diseases. The protecting effects of the MedDiet against cognitive decline have been investigated in several observational and experimental studies. Data from observational studies suggest that the MedDiet may represent an effective dietary strategy for the early prevention of dementia, although these findings require further substantiation in clinical trials which have so far produced inconclusive results. Moreover, as we discuss in this review, accumulating data emphasizes the importance of: 1) maintaining an optimal nutritional and metabolic status for the promotion of healthy cognitive aging, and 2) implementing cognition-sparing dietary and lifestyle interventions during early time-sensitive windows before the pathological cascades turn into an irreversible state. In summary, components of the MedDiet pattern, such as essential fatty acids, polyphenols and vitamins, have been associated with reduced oxidative stress and the current evidence from observational studies seems to assign to the MedDiet a beneficial role in promoting brain health; however, results from clinical trials have been inconsistent. While we advocate for longitudinal analyses and for larger and longer clinical trials to be conducted, we assert our interim support to the use of the MedDiet as a protective dietary intervention for cognitive function based on its proven cardiovascular and metabolic benefits.

Antioxidant tempol modulates the increases in tissue nitric oxide metabolites concentrations after oral nitrite administration

Nitric oxide (NO) metabolites have physiological and pharmacological importance and increasing their tissue concentrations may result in beneficial effects. Tempol (4-hydroxy-2,2,6,6-tetramethylpiperidine-N-oxyl) has antioxidant properties that may improve NO bioavailability. Moreover, tempol increases oral nitrite-derived gastric formation of S-nitrosothiols (RSNO). We hypothesized that pretreatment with tempol may further increase tissue concentrations of NO-related species after oral nitrite administration and therefore we carried out a time-dependent analysis of how tempol affects the concentrations of NO metabolites in different tissues after oral nitrite administration to rats. NO metabolites (nitrate, nitrite and RSNO) were assessed by ozone-based reductive chemiluminescence assays in plasma, stomach, aorta, heart and liver samples obtained from anesthetized rats at baseline conditions and 15 min, 30 min, 2 h or 24 h after oral nitrite (15 mg/kg) was administered to rats pretreated with tempol (18 mg/kg) or vehicle 15 min prior to nitrite administration. Aortic protein nitrosation was assessed by resin-assited capture (SNO-RAC) method. We found that pretreatment with tempol transiently enhanced nitrite-induced increases in nitrite, RSNO and nitrate concentrations in the stomach and in the plasma (all P < 0.05), particularly for 15-30 min, without affecting aortic protein nitrosation. Pretreatment with tempol enhanced nitrite-induced increases in nitrite (but not RSNO or nitrate) concentrations in the heart (P < 0.05). In contrast, tempol attenuated nitrite-induced increases in nitrite, RSNO or nitrate concentrations in the liver. These findings show that pretreatment with tempol affects oral nitrite-induced changes in tissue concentrations of NO metabolites depending on tissue type and does not increase nitrite-induced vascular nitrosation. These results may indicate that oral nitrite therapy aiming at achieving increased nitrosation of cardiovascular targets requires appropriate doses of nitrite and is not optimized by tempol.

Prolonged Administration of Rudgea viburnoides (Cham.) Benth. Prevents Impairment of Redox Status, Renal Dysfunction, and Cardiovascular Damage in 2K1C-Hypertensive Rats by Inhibiting ACE Activity and NO-GMPC Pathway Activation

Rudgea viburnoides is widely found in the Brazilian Cerrado, and commonly used in Brazilian folk medicine. In this study, we evaluated the effects of prolonged administration of the aqueous extract from R. viburnoides leaves (AERV) on impaired redox status, renal dysfunction, and cardiovascular damage in 2K1C hypertensive rats, as well as its chemical composition by LC-DAD-MS. Renal hypertension (two kidney, one-clip model) was surgically induced in male Wistar rats and AERV (30, 100 and 300 mg/kg) was administered orally five weeks after surgery for 28 days. Renal function was assessed and urinary electrolytes, pH, and density were measured. Electrocardiography, blood pressure and heart rate were recorded. Cardiac and mesenteric vascular beds were isolated for cardiac morphometry and evaluation of vascular reactivity, and aortic rings were also isolated for measurement of cyclic guanosine monophosphate levels, and the redox status was assessed. Prolonged treatment with AERV preserved urine excretion and electrolyte levels (Na+, K+, Ca2+ and Cl-), reversed electrocardiographic changes, left ventricular hypertrophy and changes in vascular reactivity induced by hypertension, and reduced blood pressure and heart rate. This effect was associated with a positive modulation of tissue redox state, activation of the NO/cGMP pathway, and inhibition of the angiotensin-converting enzyme. Glycosylated iridoids, chlorogenic acids, glycosylated triterpenes, O-glycosylated flavonols, and triterpenoid saponins were annotated. AERV showed no acute toxicity in female Wistar rats. Therefore, AERV treatment reduced the progression of cardiorenal disease in 2K1C hypertensive rats, which can be involved with an important attenuation of oxidative stress, angiotensin-converting enzyme inhibition, and activation of the NO/cGMP pathway.

Redox Switches Controlling Nitric Oxide Signaling in the Resistance Vasculature and Implications for Blood Pressure Regulation: Mid-Career Award for Research Excellence 2020

The arterial resistance vasculature modulates blood pressure and flow to match oxygen delivery to tissue metabolic demand. As such, resistance arteries and arterioles have evolved a series of highly orchestrated cell-cell communication mechanisms between endothelial cells and vascular smooth muscle cells to regulate vascular tone. In response to neurohormonal agonists, release of several intracellular molecules, including nitric oxide, evokes changes in vascular tone. We and others have uncovered novel redox switches in the walls of resistance arteries that govern nitric oxide compartmentalization and diffusion. In this review, we discuss our current understanding of redox switches controlling nitric oxide signaling in endothelial and vascular smooth muscle cells, focusing on new mechanistic insights, physiological and pathophysiological implications, and advances in therapeutic strategies for hypertension and other diseases.

Inorganic nitrate attenuates cardiac dysfunction: role for xanthine oxidoreductase and nitric oxide

Nitric oxide (NO) is a vasodilator and independent modulator of cardiac remodelling. Commonly, in cardiac disease (e.g. heart failure) endothelial dysfunction (synonymous with NO-deficiency) has been implicated in increased blood pressure (BP), cardiac hypertrophy and fibrosis. Currently no effective therapies replacing NO have succeeded in the clinic. Inorganic nitrate (NO₃ ^- ), through chemical reduction to nitrite and then NO, exerts potent BP-lowering but whether it might be useful in treating undesirable cardiac remodelling is unknown. In a nested age- and sex-matched case-control study of hypertensive patients +/- left ventricular hypertrophy (NCT03088514) we show that lower plasma nitrite concentration and vascular dysfunction accompany cardiac hypertrophy and fibrosis in patients. In mouse models of cardiac remodelling, we also show that restoration of circulating nitrite levels using dietary nitrate improves endothelial dysfunction through targeting of xanthine oxidoreductase (XOR)-driven H₂ O₂ and superoxide, and reduces cardiac fibrosis through NO-mediated block of SMAD-phosphorylation leading to improvements in cardiac structure and function. We show that via these mechanisms dietary nitrate offers easily translatable therapeutic options for treatment of cardiac dysfunction.

Aqueous extract of large cardamom inhibits vascular damage, oxidative stress, and metabolic changes in fructose-fed hypertensive rats

PURPOSE

Since metabolic abnormalities such as elevated glucose level and imbalanced lipid profiles increase the risk for hypertension and cause endothelial dysfunction, we evaluated the effect of aqueous extract of large cardamom (AELC) on fructose-induced metabolic hypertension and oxidative stress.

METHODS

The male Sprague-Dawley rats were divided into 6 groups with 5 rats in each group, and each group was fed with 10% fructose in drinking water for 8 weeks. Starting from week 5, animals were treated with 50, 100, and 200 mg/kg/day AELC or Losartan (10 mg/kg/day). Systolic, diastolic, and mean arterial blood pressure was measured once in every seven days using the tail-cuff method. Vascular function, plasma nitric oxide (NO), glucose, lipid profiles, serum biochemical, and anti-oxidant parameters were also evaluated.

RESULTS

Rats fed with fructose showed higher blood pressure, serum cholesterol, and triglyceride levels, but decreased in the AELC or Losartan treatment group. Treatments with AELC prevented exaggerated plasma glucose and oxidative stress and restored the nitric oxide level in fructose-fed rats. Besides, it also reduced vascular proliferation and improved the relaxation response of acetylcholine in the aorta pre-contracted with phenylephrine.

CONCLUSION

In summary, the obtained results suggest that AELC can prevent and reverse the high blood pressure induced by fructose, probably by restoring nitric oxide level and by improving altered metabolic parameters.

Nitrite and tempol combination promotes synergic effects and alleviates right ventricular wall stress during acute pulmonary thromboembolism

INTRODUCTION

The mechanical obstruction and pulmonary vasoconstriction are major determinants of the sudden right ventricular (RV) afterload increases observed during acute pulmonary thromboembolism (APT). Vasodilators and antioxidants agents have been shown to mitigate pulmonary hypertension. We examined whether sodium nitrite and the antioxidant tempol combination could be advantageous in an APT sheep model.

METHODS

APT was induced in anesthetized sheep by autologous blood clots (250 mg/kg) into the right atrium. Thirty minutes after APT induction, the animals received a continuous infusion of tempol (1.0 mg/kg/min), increasing sodium nitrite infusion (5, 15, and 50 μmol/kg), or a simultaneous combination of both drugs. Saline was used as a control treatment. Hemodynamic measurements were carried out every 15 min. Also, whole blood nitrite and serum 8-isoprostanes levels were measured.

RESULTS

APT induced sustained pulmonary hypertension, increased dp/dt_max, and rate pressure product (RPP). Nitrite or tempol treatments attenuated these increases (P < 0.05). When both drugs were combined, we found a robust reduction in the RV RPP compared with the treatments alone (P < 0.05). The sole nitrite infusion increased blood nitrite concentrations by 35 ± 6 μM (P < 0.05), whereas the nitrite and tempol combination produced higher blood nitrite concentrations by approximately 54 ± 7 μM. Tempol or nitrite infusions, both alone or combined, blunted the increases in 8-isoprostane concentrations observed after APT.

CONCLUSIONS

Nitrite and tempol combination protects against APT-induced RV wall stress. The association of both drugs may offer an advantage to treat RV failure during severe APT.

Direct comparison of inorganic nitrite and nitrate on vascular dysfunction and oxidative damage in experimental arterial hypertension

Arterial hypertension is one of the major health risk factors leading to coronary artery disease, stroke or peripheral artery disease. Dietary uptake of inorganic nitrite (NO₂^-) and nitrate (NO₃^-) via vegetables leads to enhanced vascular NO bioavailability and provides antihypertensive effects. The present study aims to understand the underlying vasoprotective effects of nutritional NO₂^- and NO₃^- co-therapy in mice with angiotensin-II (AT-II)-induced arterial hypertension. High-dose AT-II (1 mg/kg/d, 1w, s. c.) was used to induce arterial hypertension in male C57BL/6 mice. Additional inorganic nitrite (7.5 mg/kg/d, p. o.) or nitrate (150 mg/kg/d, p. o.) were administered via the drinking water. Blood pressure (tail-cuff method) and endothelial function (isometric tension) were determined. Oxidative stress and inflammation markers were quantified in aorta, heart, kidney and blood. Co-treatment with inorganic nitrite, but not with nitrate, normalized vascular function, oxidative stress markers and inflammatory pathways in AT-II treated mice. Of note, the highly beneficial effects of nitrite on all parameters and the less pronounced protection by nitrate, as seen by improvement of some parameters, were observed despite no significant increase in plasma nitrite levels by both therapies. Methemoglobin levels tended to be higher upon nitrite/nitrate treatment. Nutritional nitric oxide precursors represent a non-pharmacological treatment option for hypertension that could be applied to the general population (e.g. by eating certain vegetables). The more beneficial effects of inorganic nitrite may rely on superior NO bioactivation and stronger blood pressure lowering effects. Future large-scale clinical studies should investigate whether hypertension and cardiovascular outcome in general can be influenced by dietary inorganic nitrite therapy.

Omeprazole induces vascular remodeling by mechanisms involving xanthine oxidoreductase and matrix metalloproteinase activation

Proton pump inhibitors (PPI) are commonly used drugs that may increase the cardiovascular risk by mechanisms not entirely known. We examined whether the PPI omeprazole promotes vascular oxidative stress mediated by xanthine oxidoreductase (XOR) leading to activation of matrix metalloproteinases (MMPs) and vascular remodeling. We studied Wistar rats treated with omeprazole (or vehicle) combined with the XOR inhibitor allopurinol (or vehicle) for four weeks. Systolic blood pressure (SBP) measured by tail-cuff plethysmography was not affected by treatments. Omeprazole treatment increased the aortic cross-sectional area and media/lumen ratio by 25% (P < 0.05). Omeprazole treatment decreased gastric pH and induced vascular remodeling accompanied by impaired endothelium-dependent aortic responses (assessed with isolated aortic ring preparation) to acetylcholine (P < 0.05). Omeprazole increased vascular active MMP-2 expression and activity assessed by gel zymography and in situ zymography, respectively (P < 0.05). Moreover, omeprazole enhanced vascular oxidative stress assessed in situ with the fluorescent dye DHE and with the lucigenin chemiluminescence assay (both P < 0.05). All these biochemical changes caused by omeprazole were associated with increased vascular XOR activity (but not XOR expression assessed by Western blot) and treatment with allopurinol fully prevented them (all P < 0.05). Importantly, treatment with allopurinol prevented the vascular dysfunction and remodeling caused by omeprazole. Our results suggest that the long-term use of omeprazole induces vascular dysfunction and remodeling by promoting XOR-derived reactive oxygen species formation and MMP activation. These findings provide evidence of a new mechanism that may underlie the unfavorable cardiovascular outcomes observed with PPI therapy. Clinical studies are warranted to validate our findings.

Microbiota, diet and the generation of reactive nitrogen compounds

It is becoming increasingly clear that commensal bacteria inhabiting our body surfaces interact closely with the host to modulate a vast number of physiological functions. Metabolism of dietary components by gut microbiota can result in formation of a variety of reactive compounds associated with both favorable and unfavorable health effects. N-nitrosamines and trimethylamine-N-oxide (TMAO) have been associated with detrimental health effects, including increased risk of cardiovascular and metabolic disease. Contrary, bacteria-dependent formation of nitric oxide and related bioactive nitrogen oxides from dietary nitrate have been associated with salutary effects on cardiovascular function, metabolic control and more. Here we briefly discuss how the microbiota interacts with dietary factors to regulate host functions in health and disease, focusing on formation of reactive nitrogen compounds.

Nitrate and nitrite-based therapy to attenuate cardiovascular remodelling in arterial hypertension

Hypertension is a highly prevalent disease marked by vascular and cardiac maladaptive remodelling induced mainly by renin-angiotensin system activation followed by oxidative stress. Here, we briefly describe these damages and review the current evidence supporting a potential role for nitrate and nitrite as antihypertensive molecules that act via nitric oxide (NO) formation-dependent and NO formation-independent mechanisms and how nitrate/nitrite inhibits cardiovascular remodelling in hypertension. The renin-angiotensin system activation and oxidative stress converge to activate proteases involved in cardiovascular remodelling in hypertension. Besides these proteases, several investigations have demonstrated that reduced endogenous NO bioavailability is a central pathological event in hypertension. In this regard, nitrate/nitrite, long considered inert products of NO, is now known as physiological molecules able to reduce blood pressure in hypertensive patients and in different experimental models of hypertension. These effects are associated with the formation of NO and other NO-related molecules, which could induce S-nitrosylation of target proteins. However, it remains unclear whether S-nitrosylation is an essential mechanism for the anti-remodelling effects of nitrate/nitrite in hypertension. Moreover, nitrate/nitrite produces antioxidant effects associated with the inhibition of signalling pathways involved in cardiovascular remodelling. Together, these findings may help to establish nitrate and nitrite as effective therapies in hypertension-induced cardiovascular remodelling.

Long-lasting blood pressure lowering effects of nitrite are NO-independent and mediated by hydrogen peroxide, persulfides, and oxidation of protein kinase G1α redox signalling

AIMS

Under hypoxic conditions, nitrite (NO2-) can be reduced to nitric oxide (NO) eliciting vasorelaxation. However, nitrite also exerts vasorelaxant effects of potential therapeutic relevance under normal physiological conditions via undetermined mechanisms. We, therefore, sought to investigate the mechanism(s) by which nitrite regulates the vascular system in normoxia and, specifically, whether the biological effects are a result of NO generation (as in hypoxia) or mediated via alternative mechanisms involving classical downstream targets of NO [e.g. effects on protein kinase G1α (PKG1α)].

METHODS AND RESULTS

Ex vivo myography revealed that, unlike in thoracic aorta (conduit vessels), the vasorelaxant effects of nitrite in mesenteric resistance vessels from wild-type (WT) mice were NO-independent. Oxidants such as H2O2 promote disulfide formation of PKG1α, resulting in NO- cyclic guanosine monophosphate (cGMP) independent kinase activation. To explore whether the microvascular effects of nitrite were associated with PKG1α oxidation, we used a Cys42Ser PKG1α knock-in (C42S PKG1α KI; 'redox-dead') mouse that cannot transduce oxidant signals. Resistance vessels from these C42S PKG1α KI mice were markedly less responsive to nitrite-induced vasodilation. Intraperitoneal (i.p.) bolus application of nitrite in conscious WT mice induced a rapid yet transient increase in plasma nitrite and cGMP concentrations followed by prolonged hypotensive effects, as assessed using in vivo telemetry. In the C42S PKG1α KI mice, the blood pressure lowering effects of nitrite were lower compared to WT. Increased H2O2 concentrations were detected in WT resistance vessel tissue challenged with nitrite. Consistent with this, increased cysteine and glutathione persulfide levels were detected in these vessels by mass spectrometry, matching the temporal profile of nitrite's effects on H2O2 and blood pressure.

CONCLUSION

Under physiological conditions, nitrite induces a delayed and long-lasting blood pressure lowering effect, which is NO-independent and occurs via a new redox mechanism involving H2O2, persulfides, and PKG1α oxidation/activation. Targeting this novel pathway may provide new prospects for anti-hypertensive therapy.

Phloretin Ameliorates Acetic Acid Induced Colitis Through Modulation of Immune and Inflammatory Reactions in Rats

BACKGROUND

Adverse effects associated with current therapy for Ulcerative colitis (UC) over prolonged treatment periods and the high relapse rate limit their use. Incorporating fruits as regular diet has beneficial role in the management of UC. Phloretin, a dihydrochalcone of apple is reported for its anti-oxidant and anti-inflammatory effects. Our study aims to evaluate the effectiveness of phloretin on experimentally induced ulcerative colitis in rats.

METHODS

In vitro study was performed using Raw 264.7 cells stimulated with LPS (1μg/mL) and in in-vivo study, colitis was induced by intra rectal administration of 4% Acetic acid. Phloretin (50 mg/kg) was given orally for 3 days to Wistar rats after induction for the post-treatment group and 1 day before induction to the pre-treatment group. Macroscopical, biochemical and histopathological evaluations were performed to assess the effectiveness.

RESULTS

A concentration dependent inhibition of MPO and iNOS activity was obtained in LPS stimulated neutrophil cells. Phloretin exerted ameliorative effect in both pre and post-treatment groups by restoring plasma ALP and LDH level and reduce inflammatory markers like myeloperoxidase, nitric oxide and eosinophil peroxidase level as well as downregulates colon ICAM-1 gene in acetic acid induced ulcerative colitis in rats. Antioxidative potency was confirmed by restoring tissue GSH level. Phloretin prevents mucosal damage and it was confirmed by histopathological analysis.

CONCLUSION

Collectively, our findings provide evidence that phloretin might be useful as a natural therapeutic agent in the management of UC as well as may pose a promising outcome for future clinical usage.

A comprehensive time course study of tissue nitric oxide metabolites concentrations after oral nitrite administration

Nitrite and nitrate are considered nitric oxide (NO) storage pools. The assessment of their tissue concentrations may improve our understanding of how they attenuate pathophysiological mechanisms promoting disease. We hypothesized that significant differences exist when the tissue concentrations of nitrite, nitrate, and nitrosylated species (RXNO) are compared among different tissues, particularly when nitrite is administered orally because nitrite generates various NO-related species in the stomach. We studied the different time-dependent changes in plasma and tissue concentrations of nitrite, nitrate, and RXNO after oral nitrite 15 mg/kg was administered rats, which were euthanized 15, 30, 60, 120, 240, 480 or 1440 min after nitrite administration. A control group received water. Arterial blood samples were collected and the rats were perfused with a PBS solution containing NEM/DTPA to prevent the destruction of RXNO. After perfusion, heart, aorta, mesenteric artery, brain, stomach, liver and femoral muscle were harvested and immediately stored at -70°C until analyzed for their nitrite, nitrate and RXNO contents using an ozone-based reductive chemiluminescence assay. While nitrite administration did not increase aortic nitrite or nitrate concentrations for at least 60 min, both aorta and mesenteric vessels stored nitrite from 8 to 24 h after its administration and their tissue concentrations increased from 10 to 40-fold those found in plasma. In contrast, the other studied tissues showed only transient increases in the concentrations of these NO metabolites, including RXNO. The differences among tissues may reflect differences in mechanisms regulating cellular influx of nitrite. These findings have important pharmacological and clinical implications.

Modulation of mitochondria and NADPH oxidase function by the nitrate-nitrite-NO pathway in metabolic disease with focus on type 2 diabetes

Mitochondria play fundamental role in maintaining cellular metabolic homeostasis, and metabolic disorders including type 2 diabetes (T2D) have been associated with mitochondrial dysfunction. Pathophysiological mechanisms are coupled to increased production of reactive oxygen species and oxidative stress, together with reduced bioactivity/signaling of nitric oxide (NO). Novel strategies restoring these abnormalities may have therapeutic potential in order to prevent or even treat T2D and associated cardiovascular and renal co-morbidities. A diet rich in green leafy vegetables, which contains high concentrations of inorganic nitrate, has been shown to reduce the risk of T2D. To this regard research has shown that in addition to the classical NO synthase (NOS) dependent pathway, nitrate from our diet can work as an alternative precursor for NO and other bioactive nitrogen oxide species via serial reductions of nitrate (i.e. nitrate-nitrite-NO pathway). This non-conventional pathway may act as an efficient back-up system during various pathological conditions when the endogenous NOS system is compromised (e.g. acidemia, hypoxia, ischemia, aging, oxidative stress). A number of experimental studies have demonstrated protective effects of nitrate supplementation in models of obesity, metabolic syndrome and T2D. Recently, attention has been directed towards the effects of nitrate/nitrite on mitochondrial functions including beiging/browning of white adipose tissue, PGC-1α and SIRT3 dependent AMPK activation, GLUT4 translocation and mitochondrial fusion-dependent improvements in glucose homeostasis, as well as dampening of NADPH oxidase activity. In this review, we examine recent research related to the effects of bioactive nitrogen oxide species on mitochondrial function with emphasis on T2D.

Nitrates/Nitrites in Food-Risk for Nitrosative Stress and Benefits

In the context of impact on human health, nitrite/nitrate and related nitrogen species such as nitric oxide (NO) are a matter of increasing scientific controversy. An increase in the content of reactive nitrogen species may result in nitrosative stress-a deleterious process, which can be an important mediator of damage to cell structures, including lipids, membranes, proteins and DNA. Nitrates and nitrites are widespread in the environment and occur naturally in foods of plant origin as a part of the nitrogen cycle. Additionally, these compounds are used as additives to improve food quality and protect against microbial contamination and chemical changes. Some vegetables such as raw spinach, beets, celery and lettuce are considered to contain high concentrations of nitrates. Due to the high consumption of vegetables, they have been identified as the primary source of nitrates in the human diet. Processed meats are another source of nitrites in our diet because the meat industry uses nitrates/nitrites as additives in the meat curing process. Although the vast majority of consumed nitrates and nitrites come from natural vegetables and fruits rather than food additives, there is currently a great deal of consumer pressure for the production of meat products free of or with reduced quantities of these compounds. This is because, for years, the cancer risks of nitrates/nitrites have been considered, since they potentially convert into the nitrosamines that have carcinogenic effects. This has resulted in the development and rapid expansion of meat products processed with plant-derived nitrates as nitrite alternatives in meat products. On the other hand, recently, these two ions have been discussed as essential nutrients which allow nitric oxide production and thus help cardiovascular health. Thus, this manuscript reviews the main sources of dietary exposure to nitrates and nitrites, metabolism of nitrites/nitrates, and health concerns related to dietary nitrites/nitrates, with particular emphasis on the effect on nitrosative stress, the role of nitrites/nitrates in meat products and alternatives to these additives used in meat products.

Mechanisms of the protective effects of nitrate and nitrite in cardiovascular and metabolic diseases

Within the body, NO is produced by nitric oxide synthases via converting _l-arginine to citrulline. Additionally, NO is also produced via the NOS-independent nitrate-nitrite-NO pathway. Unlike the classical pathway, the nitrate-nitrite-NO pathway is oxygen independent and viewed as a back-up function to ensure NO generation during ischaemia/hypoxia. Dietary nitrate and nitrite have emerged as substrates for endogenous NO generation and other bioactive nitrogen oxides with promising protective effects on cardiovascular and metabolic function. In brief, inorganic nitrate and nitrite can decrease blood pressure, protect against ischaemia-reperfusion injury, enhance endothelial function, inhibit platelet aggregation, modulate mitochondrial function and improve features of the metabolic syndrome. However, many questions regarding the specific mechanisms of these protective effects on cardiovascular and metabolic diseases remain unclear. In this review, we focus on nitrate/nitrite bioactivation, as well as the potential mechanisms for nitrate/nitrite-mediated effects on cardiovascular and metabolic diseases. Understanding how dietary nitrate and nitrite induce beneficial effect on cardiovascular and metabolic diseases could open up novel therapeutic opportunities in clinical practice.

Therapeutic Implications of Nitrite in Hypertension

Nitrite, an anion produced from the oxidative breakdown of nitric oxide (NO), has traditionally been viewed as an inert molecule. However, this dogma has been challenged with the findings that nitrite can be readily reduced to NO under pathological conditions, hence representing a physiologically relevant storage reservoir of NO either in the blood or tissues. Nitrite administration has been demonstrated to improve myocardial function in subjects with heart failure and to lower the blood pressure in hypertensive subjects. Thus, extensive amount of work has since been carried out to investigate the therapeutic potential of nitrite in treating cardiovascular diseases, especially hypertension. Studies done on several animal models of hypertension have demonstrated the efficacy of nitrite in preventing and ameliorating the pathological changes associated with the disease. This brief review of the current findings aims to re-evaluate the use of nitrite for the treatment of hypertension and in particular to highlight its role in improving endothelial function.

Antioxidant and antihypertensive responses to oral nitrite involves activation of the Nrf2 pathway

Impaired redox balance contributes to the cardiovascular alterations of hypertension and activation of nuclear factor erythroid 2-related factor 2 (Nrf2) pathway may counteract these alterations. While nitrite recycles back to NO and exerts antioxidant and antihypertensive effects, the mechanisms involved in these responses are not fully understood. We hypothesized that nitrite treatment of two-kidney, one-clip (2K1C) hypertensive rats activates the Nrf2 pathway, promotes the transcription of antioxidant genes, and improves the vascular redox imbalance and dysfunction in this model. Two doses of oral nitrite were studied: 15 mg/kg and the sub-antihypertensive dose of 1 mg/kg. Nitrite 15 mg/kg (but not 1 mg/kg) decreased blood pressure and increased circulating plasma nitrite and nitrate. Both doses blunted hypertension-induced increases in mesenteric artery reactive oxygen species concentrations assessed by DHE technique and restored the impaired mesenteric artery responses to acetylcholine. While 2K1C hypertension decreased nuclear Nrf2 accumulation, both doses of nitrite increased nuclear Nrf2 accumulation and mRNA expression of Nrf2-regulated genes including superoxide dismutase-1 (SOD1), catalase (CAT), glutathione peroxidase (GPX), thioredoxin-1(TRDX-1) and -2 (TRDX-2). To further confirm nitrite-mediated antioxidant effects, we measured vascular SOD and GPX activity and we found that nitrite at 1 or 15 mg/kg increased the activity of both enzymes (P < 0.05). These results suggest that activation of the Nrf2 pathway promotes antioxidant effects of nitrite, which may improve the vascular dysfunction in hypertension, even when nitrite is given at a sub-antihypertensive dose. These findings may have many clinical implications, particularly in the therapy of hypertension and other cardiovascular diseases.

NADPH oxidase is a primary target for antioxidant effects by inorganic nitrite in lipopolysaccharide-induced oxidative stress in mice and in macrophage cells

Nicotinamide adenine dinucleotide phosphate (NADPH) oxidase and oxidative stress is usually considered as an important factor to the pathogenesis of various diseases. Inorganic nitrite, previously viewed as a harmful substance in our diet or inert metabolites of endogenous NO, is recently identified as an important biological NO reservoir in vasculature and tissues. Stimulation of a nitrite-NO pathway shows organ-protective effects on oxidative stress and inflammation, but the mechanisms or target are not clear. In this study, the hypothesis that inorganic nitrite attenuated lipopolysaccharide (LPS)-induced oxidative stress in mice and in macrophage cells by modulating NADPH oxidase activity and NO bioavailability were investigated. We showed that nitrite treatment, in sharp contrast with the worsening effect of NO synthases inhibition, significantly attenuated aortic oxidative stress, endothelial dysfunction and mortality in LPS-induced shock in mice. Mechanistically, protective effects of nitrite were abolished by NO scavenger and xanthine oxidase inhibitor, and inhibition of NADPH oxidase with apocynin attenuated LPS-induced oxidative stress similar to that of nitrite. In the presence of nitrite, no further effect of apocynin was observed, suggesting NADPH oxidase as a possible target. In LPS-activated macrophage cells, nitrite reduced NADPH oxidase activity and oxidative stress and these effects of nitrite were also abolished by NO scavenger and xanthine oxidase inhibitor, where xanthine oxidase-mediated reduction of nitrite attenuated NADPH oxidase activity in activated macrophages via a NO-dependent mechanism. In conclusion, these novel findings position NADPH oxidase in the inflammatory vasculature as a prime target for the antioxidant effects of inorganic nitrite, and open a new direction to modulate the inflammatory response.

Small Amounts of Inorganic Nitrate or Beetroot Provide Substantial Protection From Salt-Induced Increases in Blood Pressure

To reduce the risk of salt-induced hypertension, medical authorities have emphasized dietary guidelines promoting high intakes of potassium and low intakes of salt that provide molar ratios of potassium to salt of ≥1:1. However, during the past several decades, relatively few people have changed their eating habits sufficiently to reach the recommended dietary goals for salt and potassium. Thus, new strategies that reduce the risk of salt-induced hypertension without requiring major changes in dietary habits would be of considerable medical interest. In the current studies in a widely used model of salt-induced hypertension, the Dahl salt-sensitive rat, we found that supplemental dietary sodium nitrate confers substantial protection from initiation of salt-induced hypertension when the molar ratio of added nitrate to added salt is only ≈1:170. Provision of a low molar ratio of added nitrate to added salt of ≈1:110 by supplementing the diet with beetroot also conferred substantial protection against salt-induced increases in blood pressure. The results suggest that on a molar basis and a weight basis, dietary nitrate may be ≈100× more potent than dietary potassium with respect to providing substantial resistance to the pressor effects of increased salt intake. Given that leafy green and root vegetables contain large amounts of inorganic nitrate, these findings raise the possibility that fortification of salty food products with small amounts of a nitrate-rich vegetable concentrate may provide a simple method for reducing risk for salt-induced hypertension.

Inhibition of overexpression of Giα proteins and nitroxidative stress contribute to sodium nitroprusside-induced attenuation of high blood pressure in SHR

We earlier showed that vascular smooth muscle cells (VSMC) from spontaneously hypertensive rats (SHR) exhibit enhanced expression of Giα proteins which was attributed to the decreased levels of nitric oxide (NO), because elevation of the intracellular levels of NO by NO donors; sodium nitroprusside (SNP) and S-Nitroso-N-acetyl-DL-penicillamine (SNAP), attenuated the enhanced expression of Giα proteins. Since the enhanced expression of Giα proteins is implicated in the pathogenesis of hypertension, the present study was undertaken to investigate if treatment of SHR with SNP could also attenuate the development of high blood pressure (BP) and explore the underlying molecular mechanisms. Intraperitoneal injection of SNP at a concentration of 0.5 mg/kg body weight twice a week for 2 weeks into SHR attenuated the high blood pressure by about 80 mmHg without affecting the BP in WKY rats. SNP treatment also attenuated the enhanced levels of superoxide anion (O₂^- ), hydrogen peroxide (H₂ O₂ ), peroxynitrite (ONOO^- ), and NADPH oxidase activity in VSMC from SHR to control levels. In addition, the overexpression of different subunits of NADPH oxidase; Nox-1, Nox-2, Nox-4, P^22phox , and P^47phox , and Giα proteins in VSMC from SHR were also attenuated by SNP treatment. On the other hand, SNP treatment augmented the decreased levels of intracellular NO, eNOS, and cGMP in VSMC from SHR. These results suggest that SNP treatment attenuates the development of high BP in SHR through the elevation of intracellular levels of cGMP and inhibition of the enhanced levels of Giα proteins and nitroxidative stress.

Mechanisms impairing blood pressure responses to nitrite and nitrate

Hypertension is a multifactorial disease associated with impaired nitric oxide (NO) production and bioavailability. In this respect, restoring NO activity by using nitrite and nitrate has been considered a potential therapeutic strategy to treat hypertension. This possibility is justified by the understanding that both nitrite and nitrate may be recycled back to NO and also promote the generation of other bioactive species. This process involves a complex biological circuit known as the enterosalivary cycle of nitrate, where this anion is actively taken up by the salivary glands and converted to nitrite by nitrate-reducing bacteria in the oral cavity. Nitrite is then ingested and reduced to NO and other nitroso species under the acid conditions of the stomach, whereas reminiscent nitrite that escapes gastric reduction is absorbed systemically and can be converted into NO by nitrite-reductases in tissues. While there is no doubt that nitrite and nitrate exert antihypertensive effects, several agents can impair the blood pressure responses to these anions by disrupting the enterosalivary cycle of nitrate. These agents include dietary and smoking-derived thiocyanate, antiseptic mouthwash, proton pump inhibitors, ascorbate at high concentrations, and xanthine oxidoreductase inhibitors. In this article, we provide an overview of the physiological aspects of nitrite and nitrate bioactivation and the therapeutic potential of these anions in hypertension. We also discuss mechanisms by which agents counteracting the antihypertensive responses to nitrite and nitrate mediate their effects. These critical aspects should be taken into consideration when suggesting nitrate or nitrite-based therapies to patients.

Treatment with new organic nitrites in pulmonary hypertension of acute experimental pulmonary embolism

Acute pulmonary embolism may cause right heart failure due to increased pulmonary vascular resistance and arterial hypoxemia. Effective vasodilator therapy of the pulmonary hypertension is highly needed. Therefore, we investigated the effects of a newly developed effective pulmonary vasodilator, the organic mononitrites of 1,2-propanediol (PDNO), in a rabbit model of acute pulmonary embolism. In anesthetized and ventilated rabbits, systemic and pulmonary hemodynamics, exhaled nitric oxide (NO), plasma nitrite concentration, and blood gases were monitored. First, dose-response experiments with intravenous and left heart ventricle infusions of PDNO and inorganic nitrite were done in naive animals and in pulmonary hypertension induced by a thromboxane A2 analogue. Second, acute pulmonary embolism was induced and either PDNO or placebo were administered intravenously within 20 minutes and evaluated within 1 hour after pulmonary embolization. PDNO intravenously, in contrast to inorganic nitrite intravenously, increased exhaled NO and counteracted pulmonary hypertension and vasodilated the systemic circulation, dose-dependently, thereby showing efficient NO donation. Pulmonary embolization induced pulmonary hypertension and gas exchange disturbances. PDNO significantly decreased and normalized pulmonary vascular resistance and the right ventricle rate-pressure product, without causing tolerance, with no significant side effects on the systemic circulation, nor on blood-gas values or on methemoglobin formation. In conclusion, PDNO is a NO donor and an efficient vasodilator in the pulmonary circulation. Treatment with this or similar organic nitrites intravenously may be a future option to avoid right heart failure in life-threatening acute pulmonary embolism.

Therapeutic value of stimulating the nitrate-nitrite-nitric oxide pathway to attenuate oxidative stress and restore nitric oxide bioavailability in cardiorenal disease

Cardiovascular disorders including hypertension and associated renal disease are major health problems affecting more than 1.5 billion people worldwide. Apart from nonmodifiable factors such as ageing, family history and gender, both sedentary lifestyle and unhealthy dietary habits are considered as major risk factors. The disorders are interrelated suggesting common pathological pathways. Mechanistically, oxidative stress and compromised function of the nitric oxide synthase (NOS) system leading to endothelial dysfunction and reduction in nitric oxide (NO) bioavailability have been widely implicated and associated with development and progression of disease. New strategies that correct this redox imbalance and increase NO bioactivity may have major clinical implications. The inorganic anions, nitrate and nitrite, are endogenously formed by oxidization of NOS-derived NO, but there are also high amounts of nitrate in our daily diet. In this regard, accumulated evidence over the past two decades demonstrates that these anions can be recycled back to NO and other bioactive nitrogen oxides, thus offering an attractive alternative strategy for therapeutic exploitation. In this review, we describe how dietary stimulation of the nitrate-nitrite-NO pathway affects cardiovascular and renal functions in health and disease via modulation of oxidative stress and NO bioavailability. Clinical studies addressing potential effects on the renal system are still limited, but blood pressure-lowering effects of nitrate supplementation have been demonstrated in healthy and hypertensive subjects as well as in patients with chronic kidney disease. However, larger clinical studies are warranted to reveal whether chronic nitrate treatment can slow-down the progression of cardiorenal disease and associated complications.

Nitrite treatment downregulates vascular MMP-2 activity and inhibits vascular remodeling in hypertension independently of its antihypertensive effects

Hypertension is associated with cardiovascular remodeling. Given that impaired redox state activates matrix metalloproteinase (MMP)- 2 and promotes vascular remodeling, we hypothesized that nitrite treatment at a non-antihypertensive dose exerts antioxidant effects and attenuates both MMP-2 activation and vascular remodeling of hypertension. We examined the effects of oral sodium nitrite at antihypertensive (15 mg/kg) or non-antihypertensive (1 mg/kg) daily dose in hypertensive rats (two kidney, one clip; 2K1C model). Sham-operated and 2K1C hypertensive rats received vehicle or nitrite by gavage for four weeks. Systolic blood pressure decreased only in hypertensive rats treated with nitrite 15 mg/Kg/day. Both low and high nitrite doses decreased 2K1C-induced vascular remodeling assessed by measuring aortic cross-sectional area, media/lumen ratio, and number of vascular smooth muscle cells/aortic length. Both low and high nitrite doses decreased 2K1C-induced vascular oxidative stress assessed in situ with the fluorescent dye DHE and with the lucigenin chemiluminescence assay. Vascular MMP-2 expression and activity were assessed by gel zymography, Western blot, and in situ zymography increased with hypertension. While MMP-2 levels did not change in response to both doses of nitrite, both doses completely prevented hypertension-induced increases in vascular MMP activity. Moreover, incubation of aortas from hypertensive rats with nitrite at 1-20 μmol/L reduced gelatinolytic activity by 20-30%. This effect was fully inhibited by the xanthine oxidase (XOR) inhibitor febuxostat, suggesting XOR-mediated generation of nitric oxide (NO) from nitrite as a mechanism explaining the responses to nitrite. In vitro incubation of aortic extracts with nitrite 20 μmol/L did not affect MMP-2 activity. These results show that nitrite reverses the vascular structural alterations of hypertension, independently of anti-hypertensive effects. This response is mediated, at least in part, by XOR and is attributable to antioxidant effects of nitrite blunting vascular MMP-2 activation. Our findings suggest nitrite therapy to reverse structural alterations of hypertension.

AMP-activated protein kinase activation and NADPH oxidase inhibition by inorganic nitrate and nitrite prevent liver steatosis

Liver steatosis, or fatty liver, is the most common liver disease in the world, affecting up to 25% of all Americans. There is currently no approved drug available for this condition, which may progress to serious disease, including steatohepatitis, fibrosis, and cirrhosis. Here, we show in rodent and human models of metabolic syndrome that steatosis can be prevented by a simple dietary approach. Inorganic nitrate, present in green leafy vegetables, is converted in vivo to nitric oxide (NO) in a process involving symbiotic host bacteria. NO then induces key metabolic regulatory pathways to ultimately reduce oxidative stress and improve cardiometabolic functions. Clinical trials would be helpful to tell if dietary nitrate is useful in treatment and prevention of fatty liver disease.

Advanced age and unhealthy dietary habits contribute to the increasing incidence of obesity and type 2 diabetes. These metabolic disorders, which are often accompanied by oxidative stress and compromised nitric oxide (NO) signaling, increase the risk of adverse cardiovascular complications and development of fatty liver disease. Here, we investigated the therapeutic effects of dietary nitrate, which is found in high levels in green leafy vegetables, on liver steatosis associated with metabolic syndrome. Dietary nitrate fuels a nitrate–nitrite–NO signaling pathway, which prevented many features of metabolic syndrome and liver steatosis that developed in mice fed a high-fat diet, with or without combination with an inhibitor of NOS (l-NAME). These favorable effects of nitrate were absent in germ-free mice, demonstrating the central importance of host microbiota in bioactivation of nitrate. In a human liver cell line (HepG2) and in a validated hepatic 3D model with primary human hepatocyte spheroids, nitrite treatment reduced the degree of metabolically induced steatosis (i.e., high glucose, insulin, and free fatty acids), as well as drug-induced steatosis (i.e., amiodarone). Mechanistically, the salutary metabolic effects of nitrate and nitrite can be ascribed to nitrite-derived formation of NO species and activation of soluble guanylyl cyclase, where xanthine oxidoreductase is proposed to mediate the reduction of nitrite. Boosting this nitrate–nitrite–NO pathway results in attenuation of NADPH oxidase-derived oxidative stress and stimulation of AMP-activated protein kinase and downstream signaling pathways regulating lipogenesis, fatty acid oxidation, and glucose homeostasis. These findings may have implications for novel nutrition-based preventive and therapeutic strategies against liver steatosis associated with metabolic dysfunction.

Redox regulation and NO/cGMP plus K+ channel activation contributes to cardiorenal protection induced by Cuphea carthagenensis (Jacq.) J.F. Macbr. in ovariectomized hypertensive rats

BACKGROUND

One of the medicinal plants widely used by the population in the treatment of hypertension, atherosclerosis and circulatory disorders is Cuphea carthagenensis (Jacq.) J.F. Macbr. (Lythraceae), popularly known as 'sete sangrias', being found in Brazil, Hawaii and in South Pacific Islands. Despite the widespread use of this species by the population, its long-term antihypertensive and cardioprotective activities have not yet been scientifically evaluated.

PURPOSE

To evaluate the possible cardioprotective effects of an ethanol-soluble fraction obtained from C. carthagenensis (ESCC) using ovariectomized hypertensive rats to simulate a broad part of the female population over 50 years of age affected by hypertension. In addition, the molecular mechanism that may be responsible for its cardiorenal protective effects was also explored.

METHODS

Female Wistar rats were submitted to surgical procedures of bilateral ovariectomy and induction of renovascular hypertension (two-kidneys, one-clip model). The sham-operated group was used as negative control. ESCC was obtained and a detailed phytochemical investigation about its main secondary metabolites was performed. ESCC was orally administered at doses of 30, 100 and 300  mg/kg, daily, for 28 days, 5 weeks after surgery. Enalapril (15  mg/kg) was used as standard antihypertensive drug. Renal function was evaluated on days 1, 7, 14, 21 and 28. At the end of the experimental period, systolic, diastolic, mean arterial pressure and heart rate were recorded. The activity of the tissue enzymatic antioxidant system, thiobarbituric acid reactive substances, nitrotyrosine, nitrite, aldosterone and vasopressin levels, in addition to the activity of the angiotensin-converting enzyme were also evaluated. Additionally, vascular reactivity to acetylcholine, sodium nitroprusside, and phenylephrine, and the role of nitric oxide, prostaglandins, and K⁺ channels in the vasodilator response of ESCC on the mesenteric vascular bed were also investigated.

RESULTS

ESCC-treatment induced an important cardiorenal protective response, preserving renal function and preventing elevation of blood pressure and heart rate in ovariectomized hypertensive rats. In addition, prolonged treatment with ESCC recovered mesenteric vascular reactivity at all doses used. This effect was associated with an important modulation of the antioxidant defense system with a possible increase in NO bioavailability. Additionally, NO/cGMP activation and K⁺ channel opening-dependent vasodilator effect was observed on the mesenteric vascular bed, indicating a potential mechanism for the cardiovascular effects of ESCC.

CONCLUSION

A 28-days ESCC treatment reduces the progression of the cardiorenal disease in ovariectomized hypertensive rats. These effects seem to be involved with an attenuation of oxidative and nitrosative stress, affecting endothelial nitric oxide production and K⁺ channel opening in smooth muscle cells.

Protective effects of sodium nitrate against testicular apoptosis and spermatogenesis impairments in streptozotocin-induced diabetic male rats

AIMS

As nitric oxide (NO) production is essential for insulin signaling, glucose uptake, endothelial function, and regulation of apoptosis, the loss of bioavailable NO may be a mechanism underlying the development of diabetes complication. Dietary nitrate acts as a substrate for NO generation, thus serving as a physiological source of NO. This study evaluated the therapeutic effects of nitrate supplementation on the apoptosis-induced testicular disorders in diabetic rats.

MAIN METHODS

Fifty male Wistar rats were divided into five groups; control, control with 100 mg/L nitrate in distilled drinking water, diabetes, diabetes treated with 2-4 U/day NPH insulin, diabetes treated with 100 mg/L nitrate in distilled drinking water. After 8 weeks, blood samples, testis, and epididymis were collected to assess the apoptosis process and the stereology of testis tissue, sperm motility, morphology and DNA fragmentation, and also mRNA expression of miR-449a, p53, Pdcd4, and Pacs2 mRNA, as well as serum glucose, insulin, and NOx levels were investigated.

KEY FINDINGS

The results of this study indicated that nitrate treatment ameliorated the sperm parameters, testicular morphometrical and stereological alterations, reduced blood glucose, the number of TUNEL positive cells and tubules, and testicular expressions of p53, Pdcd4, and Pacs2 mRNA as well as increased body weight, serum insulin and NOx levels, and testicular expression of miR-449a in streptozotocin-induced diabetic rats.

SIGNIFICANCE

Our in vivo evidence revealed that nitrate treatment may has a favorable effect as an exogenous NO donor on experimental diabetic testicular damages in which NO bioavailability is impaired.

Mechanisms underlying blood pressure reduction by dietary inorganic nitrate

Nitric oxide (NO) importantly contributes to cardiovascular homeostasis by regulating blood flow and maintaining endothelial integrity. Conversely, reduced NO bioavailability is a central feature during natural ageing and in many cardiovascular disorders, including hypertension. The inorganic anions nitrate and nitrite are endogenously formed after oxidation of NO synthase (NOS)-derived NO and are also present in our daily diet. Knowledge accumulated over the past two decades has demonstrated that these anions can be recycled back to NO and other bioactive nitrogen oxides via serial reductions that involve oral commensal bacteria and various enzymatic systems. Intake of inorganic nitrate, which is predominantly found in green leafy vegetables and beets, has a variety of favourable cardiovascular effects. As hypertension is a major risk factor of morbidity and mortality worldwide, much attention has been paid to the blood pressure reducing effect of inorganic nitrate. Here, we describe how dietary nitrate, via stimulation of the nitrate-nitrite-NO pathway, affects various organ systems and discuss underlying mechanisms that may contribute to the observed blood pressure-lowering effect.

Metabolic Effects of Dietary Nitrate in Health and Disease

Nitric oxide (NO), generated from L-arginine and oxygen by NO synthases, is a pleiotropic signaling molecule involved in cardiovascular and metabolic regulation. More recently, an alternative pathway for the formation of this free radical has been explored. The inorganic anions nitrate (NO₃^-) and nitrite (NO₂^-), originating from dietary and endogenous sources, generate NO bioactivity in a process involving seemingly symbiotic oral bacteria and host enzymes in blood and tissues. The described cardio-metabolic effects of dietary nitrate from experimental and clinical studies include lowering of blood pressure, improved endothelial function, increased exercise performance, and reversal of metabolic syndrome, as well as antidiabetic effects. The mechanisms underlying the salutary metabolic effects of nitrate are being revealed and include interaction with mitochondrial respiration, activation of key metabolic regulatory pathways, and reduction of oxidative stress. Here we review the recent advances in the nitrate-nitrite-NO pathway, focusing on metabolic effects in health and disease.

Nitrite exerts antioxidant effects, inhibits the mTOR pathway and reverses hypertension-induced cardiac hypertrophy

Cardiac hypertrophy is a common consequence of chronic hypertension and leads to heart failure and premature death. The anion nitrite is now considered as a bioactive molecule able to exert beneficial cardiovascular effects. Previous results showed that nitrite attenuates hypertension-induced increases in reactive oxygen species (ROS) production in the vasculature. Whether antioxidant effects induced by nitrite block critical signaling pathways involved in cardiac hypertrophy induced by hypertension has not been determined yet. The Akt/mTOR signaling pathway is responsible to activate protein synthesis during cardiac remodeling and is activated by increased ROS production, which is commonly found in hypertension. Here, we investigated the effects of nitrite treatment on cardiac remodeling and activation of this hypertrophic signaling pathway in 2 kidney-1 clip (2K1C) hypertension. Sham and 2K1C rats were treated with oral nitrite at 1 or 15 mg/kg for four weeks. Nitrite treatment (15 mg/kg) reduced systolic blood pressure and decreased ROS production in the heart tissue from hypertensive rats. This nitrite dose also blunted hypertension-induced activation of mTOR pathway and cardiac hypertrophy. While the lower nitrite dose (1 mg/kg) did not affect blood pressure, it exerted antioxidant effects and tended to attenuate mTOR pathway activation and cardiac hypertrophy induced by hypertension. Our findings provide strong evidence that nitrite treatment decreases cardiac remodeling induced by hypertension as a result of its antioxidant effects and downregulation of mTOR signaling pathway. This study may help to establish nitrite as an effective therapy in hypertension-induced cardiac hypertrophic remodeling.

Regulation of vascular tone homeostasis by NO and H2S: Implications in hypertension

Nitric oxide (NO) and hydrogen sulfide (H2S) are two gasotransmitters that are produced in the vasculature and contribute to the regulation of vascular tone. NO and H2S are synthesized in both vascular smooth muscle and endothelial cells; NO functions primarily through the sGC/cGMP pathway, and H2S mainly through activation of the ATP-dependent potassium channels; both leading to relaxation of vascular smooth muscle cells. A deficit in the NO/H2S homeostasis is involved in the pathogenesis of various cardiovascular diseases, especially hypertension. It is now becoming increasingly clear that there are important interactions between NO and H2S and that have a profound impact on vascular tone and this may provide insights into the new therapeutic interventions. The aim of this review is to provide a better understanding of individual and interactive roles of NO and H2S in vascular biology. Overall, available data indicate that both NO and H2S contribute to vascular (patho)physiology and in regulating blood pressure. In addition, boosting NO and H2S using various dietary sources or donors could be a hopeful therapeutic strategy in the management of hypertension.

Effects of long-term nitrate supplementation on carbohydrate metabolism, lipid profiles, oxidative stress, and inflammation in male obese type 2 diabetic rats

PURPOSE

Supplementation with inorganic nitrate to boost the nitrate-nitrite-nitric oxide (NO) pathway, may act as a potential therapeutic agent in diabetes. The aim of this study was to determine the effects of nitrate on carbohydrate metabolism, lipid profiles, oxidative stress, and inflammation in obese type 2 diabetic rats.

METHODS

Male Wistar rats were divided into 4 groups: Control, control + nitrate, diabetes, and diabetes + nitrate. Diabetes was induced using a high-fat diet and low-dose of streptozotocin. Sodium nitrate (100 mg/L in drinking water) was administered simultaneously for two months. Serum levels of fasting glucose, insulin, and lipid profiles were measured every 2-weeks. Glycated hemoglobin (HbA1c) was measured monthly. Serum thiobarbituric reactive substances (TBARS) level and catalase activity were measured before and after treatment. At the end of the study, glucose, pyruvate, and insulin tolerance tests were done. Glucose-stimulated insulin secretion (GSIS) and insulin content from isolated pancreatic islets were also assessed; mRNA expression of iNOS as well as mRNA expression and protein levels of GLUT4 in insulin-sensitive tissues, and serum IL-1β were determined.

RESULTS

Nitrate supplementation in diabetic rats significantly improved glucose tolerance, lipid profiles, and catalase activity as well as decreased gluconeogenesis, fasting glucose, insulin, and IL-1β; although it had no significant effect on GSIS, islet insulin content, HbA1c, and serum TBARS. Compared to the controls, in diabetic rats, mRNA expression and protein levels of GLUT4 were significantly lower in the soleus muscle (54% and 34%, respectively) and epididymal adipose tissue (67% and 41%, respectively). In diabetic rats, nitrate administration increased GLUT4 mRNA expression and protein levels in both soleus muscle (215% and 17%, respectively) and epididymal adipose tissue (344% and 22%, respectively). In diabetic rats, nitrate significantly decreased elevated iNOS mRNA expression in both the soleus muscle and epididymal adipose tissue.

CONCLUSION

Chronic nitrate supplementation in obese type 2 diabetic rats improved glucose tolerance, insulin resistance, and dyslipidemia; these favorable effects were associated with increased mRNA and protein expression of GLUT4 and decreased mRNA expression of iNOS in insulin-sensitive tissues, and with decreased gluconeogenesis, inflammation, and oxidative stress.

Maternal hypertension and feto-placental growth restriction is reversed by sildenafil: Evidence of independent effects of circulating nitric oxide levels

Sildenafil has shown nitric oxide (NO)-independent pleiotropic effects, however the mechanisms involved are unclear. We investigated the protective effects of sildenafil against hypertension in pregnancy and feto-placental growth restriction induced by NO inhibition, and if sodium nitrite-derived NO formation influences sildenafil effects. We evaluated the plasmatic levels of NO metabolites, cyclic guanosine monophosphate (cGMP), oxidative stress and myeloperoxidase, which are involved in endothelial dysfunction during hypertension in pregnancy. Also, we performed in vitro experiments to examine cell viability and NO synthesis in human umbilical vein endothelial cells (HUVECs) cultures incubated with plasma from healthy or hypertensive pregnant rats treated (or not) with both drugs, either alone or in association. Sildenafil blunted hypertension in pregnancy and protected against feto-placental growth restriction induced by NO inhibition and these effects of sildenafil alone were similar to those presented by its association with sodium nitrite. Protective effects of sildenafil were observed even with low plasmatic NO levels and were not followed by increases in cGMP levels. Also, sildenafil, but not sodium nitrite, blunted the increases in myeloperoxidase activity. Both drugs (isolated or in association) presented antioxidant effects. Plasma from hypertensive pregnant rats treated with sildenafil, but not sodium nitrite alone, increased the viability of HUVECs. NO synthesis in HUVECs cultures was increased with plasma from rats treated with both drugs. We conclude that sildenafil effects are not dependent of circulating NO levels in hypertension and feto-placental growth restriction. These findings may reflect a protection against myeloperoxidase and pro-oxidant activation in hypertension in pregnancy.